1. Field of the Invention
This invention relates to a method for reducing the wall fouling normally occurring in stainless steel reactors used for the suspension polymerization of vinyl chloride containing monomer systems.
2. Description of the Prior Art
Wall fouling in reactors used for the suspension polymerization of vinyl chloride systems has been a problem, and particularly so in recent years because of the tight constraints imposed on vinyl chloride emission to the atmosphere. Several obvious advantages would be achieved by reducing wall fouling. First, productivity of the reactors could be increased in that the reactors would not have to be taken out of service as often for cleaning. Second, there is less product contamination due to particulate material dropping from the reactor surface into the product.
Some of the techniques used in reducing polymer deposit in the polymerization of vinyl chloride are described in the following patents:
U.S. Pat. No. 3,778,423 discloses a process for reducing polymer deposit in a glass lined reactor by wetting the reactor surface with a solution containing a free radical inhibitor, e.g., a polar organic compound such as alpha-methyl styrene or a chain terminating agent such as an amine, e.g., ethylenediamine tetraacetic acid; fatty acids, an aldehyde such as acrolein, methacrolein and a conjugated diolefin such as isoprene or butadiene.
U.S. Pat. No. 3,562,238 discloses a process for reducing reactor wall fouling in vinyl chloride polymerization by incorporating less than 1,000 ppm (based on the monomers) of magnesium hydroxide in the polymer recipe.
U.S. Pat. No. 3,926,910 discloses a method for reducing reactor wall fouling in vinyl chloride polymerization processes by incorporating from about 0.001 to about 0.02 parts of a nitrite salt per 100 parts monomer onto the reactor surface prior to forming resinous material. The nitrite can be included in the polymerization recipe or sprayed onto the reactor surface as an aqueous solution.
U.S. Pat. No. 3,842,055 discloses a process for reducing reactor wall fouling in the suspension polymerization of vinyl chloride by spraying a fine stream of water in an amount of 20-100% volume of the volume of monomers onto the reactor dome during polymerization.
U.S. Pat. No. 3,669,946 discloses a method for preventing polymer deposition on reactor walls and equipment by coating the surfaces with a polar organic compound such as benzene or ethanol. Example 1 shows applying the solvent to the reactor surfaces and then drying the solvent therefrom. Example 7 in the patent shows that small additions of a caustic soda solution, e.g., in the amount of 0.1% based on vinyl chloride content, give some improvement in reducing polymer deposition.
U.S. Pat. No. 4,024,301 discloses the addition of a branched polymerization amine such as o-phenylene diamine as a coating for the reactor surface.
U.S. Pat. No. 3,997,707 discloses the addition of oxalic acid or its salt to the polymerization recipe in an effort to reduce wall fouling.